Catheters are designed for-insertion into vessels including coronary arteries, tubes including tracheas, uterine tubes and ureters, and internal organs so as to permit injection or evacuation of fluids or to maintain the openness of a passageway.
Flexible catheters generally used are made of a resilient or elastic material throughout the whole length. While such flexible catheters are inserted into passageways or body cavities of relatively simple structures without any difficulty, they are not smoothly inserted into those of complicated structures due to their total flexibility.
Our study has proved that a catheter, which is smoothly inserted into the body should possess adequate flexibility and elasticity on its insertion end (hereinafter referred to as flexible portion), and rigidity sufficient for effective torque transmission on its base (hereinafter referred to as torque transmitting portion).
The rigid torque transmitting portion of a catheter is useful for easy and smooth insertion of the flexible portion into the vicinity of the target regions such as vessels and internal organs. Furthermore, the torque transmitting portion efficiently transmits torque, which is generated by rotating a handle of the catheter (non-inserted portion adjacent to the torque transmitting portion), to the flexible portion, so that the running direction of the flexible portion is appropriately adjusted from the vicinity of the target regions to the final target portion.
On the other hand, appropriate flexibility is required on the flexible portion. Otherwise, the flexible portion would not easily follow the movement of the torque transmitting portion corresponding to the torque generated by rotation of the handle into a direction and at an angle desired when adjusting the direction and angle of the inserted catheter after insertion or during insertion of the catheter, or it may hurt tissues of vessels or internal organs upon insertion thereof.
Heretofore, catheters having both the torque transmitting ability of the torque transmitting portion and flexibility of the flexible portion have been proposed. For example, Japanese Published Patent Application No. Sho 54-8036, "Plastic tube used for medical purposes" discloses a catheter having a flexible portion and a rigid portion. Although appropriate flexibility is required on the flexible portion as described above, consistent flexibility of the flexible portion before insertion causes undesirable bent thereof due to friction against the wall of insertion guide tubes or the wall of passageways in the body during insertion to the target region, giving rise to difficulty in inserting smoothly. Appropriate rigidity is desirable on the flexible portion for easy and smooth insertion. The rigid flexible portion may, however, hurt the passageways. In other words, the flexible portion should possess conflicting properties, i.e., flexibility and rigidity.
The object of this invention is accordingly to provide an improved catheter, which is easily and smoothly inserted into the body, has efficient torque transmitting ability to a flexible portion, and does not hurt inside of the body by the flexible portion.